Just an update if anyone is curious... I picked up the PHA-2 tonight and it sounds awesome with the 5s/SE846's... Soundstage is sooooo wide.. :)

EDIT:

Well, I thought it sounded awesome, but, I think that was just me trying to convince myself that I invested $600 smartly.. I didn't.. I don't think the PHA-2 really adds any value to the SE846 when paired with the 5s.. I really think that these headphones are just so efficient they don't need an external AMP... In some cases I actually found the PHA-2 made the bass a bit muddy and unnatural..